1. Field of the Invention
The present invention relates to a bidirectional digital wireless system transmitting and receiving asymmetric transmission frames, and more particularly to a bidirectional digital wireless system transmitting and receiving uplink transmission frames and downlink transmission frames wherein the downlink transmission frames are asymmetric to the respective uplink transmission frames with respect to time length.
2. Description of the Related Art
Up until now, there have been proposed a wide variety of bidirectional digital wireless systems, one typical type of which is disclosed in Japanese Laid-Open Patent Application No. H10-150692. Such conventional bidirectional digital wireless system is shown in FIG. 20 as comprising a conventional mobile station 1 and a conventional base station 2.
As shown in FIG. 20, the conventional mobile station 1 comprises a microphone 3, an analog sound signal processing circuit 4, an A-D converter 5, a noise canceller 6, a sound encoding unit 7, an ECC encoding unit 8, a digital modulating unit 9, a sound information transmitting high frequency circuit 10, hereinlater simply referred to as “a sound information transmitting HF circuit 10”, a radio frequency transmitting and receiving switching unit 11, hereinlater simply referred to as “a RF transmitting and receiving switching unit 11”, a transmitting antenna 61A, a control information receiving high frequency circuit 12, a demodulating unit 13, a system controller 14, a power supply circuit 15, a battery 16, a state indicating unit 17, and a mode switching unit 18.
The microphone 3 is operative to collect an analog sound signal s1 to be converted to an electric signal, i.e., a microphone output signal s2 containing sound components. The analog sound signal processing circuit 4 is operative to process the microphone output signal s2 in terms of, for example, a signal level to output an analog sound signal s3. The A-D converter 5 is operative to convert the analog sound signal s3 into a PCM digital signal s4. The noise canceller 6 is operative to input the PCM digital signal s4 from the A-D converter 5 and cancel noise components such as, for example, ambient noises, from the PCM digital signal s4 to output a noise canceller output s5. The sound encoding unit 7 is operative to encode the noise canceller output s5 into a sound compressed signal s6 at a bit rate lower than that of the noise canceller output s5. The sound encoding unit 7 carries out a Variable Bit Rate (VBR) encoding method. Preferably, the sound encoding unit 7 may encode the noise canceller output s5 into the sound compressed signal s6 in an encoding manner such as, for example, subband encoding, ADPCM (Adaptive Differential Pulse Code Modulation) encoding, or subband ADPCM encoding, so as to realize a delay time appropriate for use of, for example, amplifying the sound components contained in the signal. The ECC encoding unit 8 is operative to perform error correcting coding, interleave process, and, if necessary, error detecting coding to the sound compressed signal s6, and then perform line coding to thus processed sound compressed signal s6 by adding information necessary for transmission such as, for example, bidirectional communication, line connection and synchronous processing to output a transmission frame signal s7. The digital modulating unit 9 is operative to modulate and convert from digital to analog forms the transmission frame signal s7 to output a digital modulated signal s8. The digital modulating unit 9 may modulate the transmission frame signal s7 in a manner such as, for example, /4 PSK (Phase-Shift Keying), 8 PSK, MSK (Minimum Shift Keying), or QAM (Quadrature Amplitude Modulation) modulation. Furthermore, the digital modulating unit 9 is operative to limit a bandwidth of the transmission frame signal s7 by means of, for example, Nyquist filtering or Gaussian filtering to prevent interference between codes. In general, the digital modulating unit 9 is operative to allocate bandwidths to uplink and downlink traffics evenly. It is needless to mention that the digital modulating unit 9 may adjust a bandwidth ratio of a bandwidth to be allocated to uplink traffic, viz., “uplink bandwidth” to a bandwidth to be allocated to downlink traffic, viz., “downlink bandwidth” to any value.
Alternatively, digital processes performed by the sound encoding unit 7, the ECC encoding unit 8, and the digital modulating unit 9 may be integrally carried out by a single process such as, for example, a Trellis coding process. The sound information transmitting HF circuit 10 is operative to have the digital modulated signal s8 carried on a carrier frequency of a transmission channel, and then limit a bandwidth of and amplify to a predetermined transmission level the digital modulated signal s8 thus carried on the carrier frequency of the transmission channel to generate a sound information transmission output signal s9.
The RF transmitting and receiving switching unit 11 is operative to extract a receiving control signal d4 from the sound information transmission output signal s9 in accordance with the mobile system control signal ctx14 outputted from the system controller 14A and output the receiving control signal d4 to the control information receiving HF circuit 12. This means that the RF transmitting and receiving switching unit 11 is operative to control a timing of the sound information transmission output signal s9 on the basis of the mobile system control signal ctx14 outputted from the system controller 14A with respect to a time scale in a Time Division Multiplex (TDM) bidirectional system to extract the receiving control signal d4 while, on the other hand, the RF transmitting and receiving switching unit 11 is operative to control a timing of the sound information transmission output signal s9 by means of, for example, frequency filtering, or coupling circuits, in a Frequency Division Multiplex bidirectional system to extract the receiving control signal d4. The sound information transmission output signal s9 is then emitted to the air through the transmitting antenna 51A. The sound information transmission output signal s9 is received by the base station 2.
The sound information transmission output signal s9 is received by the conventional base station 2.
As best shown in FIG. 20, the conventional base station 2 comprises a receiving antenna 61B, a radio frequency transmitting and receiving switching unit 20, hereinlater simply referred to as “RF transmitting and receiving switching unit 20”, a sound information receiving high frequency circuit 21, hereinlater simply referred to as a “sound information receiving HF circuit 21”, a digital demodulating unit 22, a ECC decoding unit 23, a sound decoding unit 24, a D-A converter 25, an analog sound processing circuit 26, an analog sound output terminal 27, a control information transmitting high frequency circuit 28, a modulating unit 29, a system controller 30, a power supply circuit 31, an external power input terminal 32, an external power source p3, a mode switching unit 33, state indicating unit 34, a digital sound information outputting unit 35, and an external control data I/O unit 36.
The receiving antenna 61B of base station 2 is operative to receive sound information transmission output signal s9 and output a sound information receiving input signal s12 to the RF transmitting and receiving switching unit 20. The RF transmitting and receiving switching unit 20 is operative to receive the sound information receiving input signal s12 in a reverse manner to the RF transmitting and receiving switching unit 11 of the conventional mobile station 1 as described hereinearlier to output the sound information receiving input signal s12. The sound information receiving HF circuit 21 is operative to amplify the sound information receiving input signal s12 to a predetermined level and limit a bandwidth of the sound information receiving input signal s12 to output a baseband signal s13. The sound information receiving HF circuit 21 may process the sound information receiving input signal s12 by means of, for example, double/single super heterodyne system, or direct conversion system. Furthermore, the baseband signal s13 may be obtained by means of intermediate frequency D-A converting method such as, for example, IF (Intermediate Frequency) sampling.
The digital demodulating unit 22 is operative to demodulate the base band signal s13 to output a digital demodulated signal s14.
With regard to the processes performed by sound information receiving HF circuit 21 and the digital demodulating unit 22, space diversity may be carried out. This means that the conventional base station 2 may comprise a plurality of sound information receiving HF circuits 21 and digital demodulating units 22 wherein the numbers of sound information receiving HF circuits 21 and digital demodulating units 22 are equal to the number of diversity branches.
The ECC decoding unit 23 is operative to detect and analyze the information added in the digital demodulated signal s14. The ECC decoding unit 23 is operative to perform de-interleave, error detecting and correcting processes to the digital demodulated signal s14 with reference to the information thus detected and analyzed to output an error corrected signal s15. The sound decoding unit 24 is operative to decode the error corrected signal s15 into a reconstructed PCM digital signal s16. The sound decoding unit 24 carries out a Variable Bit Rate (VBR) decoding method.
The D-A converter 25 is operative to convert the reconstructed PCM digital signal s16 from digital to analog forms to output a D-A converted output signal s17. The analog sound processing circuit 26 is operative to amplify the D-A converted output signal s17 to a predetermined level to output an analog sound signal s18 through the analog sound output terminal 27 from the conventional base station 2.
The sound information transmission output signal s9 emitted from the conventional mobile station 1 and the sound information receiving input signal s12 outputted from the RF transmitting and receiving switching unit 20 of the conventional base station 2 will be hereinlater simply referred to as “uplink information” and “downlink information” in the bidirectional communication system, respectively.
The system controller 14 of the conventional mobile station 1 is operative to manage each of elements constituting the conventional mobile station 1 by inputting and outputting mobile system control signals ctx1 through ctx14 from and to the constituent elements including the microphone 3 through the mode switching unit 18.
Similarly, the system controller 30 of the conventional base station 2 is operative to manage each of elements constituting the conventional base station 2 by inputting and outputting base system control signals crx1 through ctx16 from and to the constituent elements including the antenna 61B through the external control data I/O unit 36.
The description hereinlater will be directed to bidirectional transmission frames transmitted and received between the conventional mobile station 1 and the conventional base station 2 with reference to FIG. 21.
The transmission frame signal s7 generated by the ECC encoding unit 8 and to be inputted to the digital modulating unit 9 is shown in FIG. 21 as comprising an uplink transmission frame, hereinlater simply referred to as “UL transmission frame no.1P”, and a downlink transmission frame, hereinlater simply referred to as “DL transmission frame no. 2P”. The UL transmission frame no.1P carries main information transmitted from the conventional mobile station 1 to the conventional base station 2 through an uplink transmission line, hereinlater simply referred to as “uplink” and the DL transmission frame no. 2P carries subsidiary information transmitted from the conventional base station 2 to the conventional mobile station 1 through a downlink transmission line, hereinlater simply referred to as “downlink” wherein the main information and the subsidiary information are transmitted by Time Division Multiplexing.
The UL transmission frame no.1P and the DL transmission frame no. 2P include preamble frame portions UL-Pre and DL-Pre, unique word frame portions UL-UW and DL-UW, and control information frame portions UL-Ctrl and DL-Ctrl, respectively. The UL transmission frame no. 1P further includes a main information frame portion UL-Data.
The downlink control information frame portion DL-Ctrl of the DL transmission frame no. 2P may include a pilot signal indicating a receive level as transmit power control information to be used in open loop power control.
The UL transmission frame no.1P and the DL transmission frame no. 2P further include bidirectional guard frame portions DLGuard and ULGuard, respectively. The guard frame portions should be designed to be inserted in the respective transmission frames in consideration of various factors such as, for example, delay times resulting from operations performed in high frequency circuits and radio transmission paths. The main information segment may be, for example, a sound signal segment, which is required to be replayed immediately. The subsidiary information segment d12 may be, for example, an instruction to execute a function or to implement a mode, which is to be visually indicated, and not required to be replayed immediately. Preferably, the frame length of an uplink transmission frame should be 1 to 2 milliseconds or less to realize a requirement of a wireless microphone system for real time replay. The downlink transmission frame is equal to the uplink transmission frame with respect to time length. In other words, the uplink transmission frame is “symmetric” to the downlink transmission frame with respect to time length. This means the frame length of a downlink transmission frame is equal to that of the uplink transmission frame, which should be 1 to 2 milliseconds or less.
The conventional bidirectional digital wireless system, however, encounters a drawback that the conventional bidirectional digital wireless system degrades a frequency utilization efficiency due to the fact that a large amount of downlink information is required to be transmitted on the downlink transmission frame, which is symmetric to the uplink transmission frame with respect to time length, and therefore not optimized to transmit the large amount of information.
The conventional bidirectional digital wireless system encounters another drawback that the conventional bidirectional digital wireless system degrades a frequency utilization efficiency when mobile station transmission power control of open loop type is executed due to the fact that a plurality of unmodulated pilot signals are required to be separately transmitted on the downlink transmission frame, which is symmetric to the uplink transmission frame with respect to time length, and therefore not optimized to transmit the downlink transmission frame containing the unmodulated pilot signals.
Furthermore, the conventional bidirectional digital wireless system encounters another drawback that the conventional bidirectional digital wireless system degrades a frequency utilization efficiency when error correcting, time diversity transmission, or automatic retransmission request process is executed to ensure reliable quality of downlink information due to the increase in an amount of control information to be transmitted on the uplink transmission frame and a downlink transmission frame.